A dispersion-managed optical transmission line has been proposed as a long-haul optical transmission line such as a submarine cable. In the dispersion-managed optical transmission line, a wavelength dispersion of the optical transmission line is managed by combining a positive-dispersion optical fiber having a positive wavelength-dispersion and a negative-dispersion optical fiber having a negative wavelength-dispersion at a wavelength of a signal light.
A technology of transmitting a 40-Gb/s optical signal over a distance of 6,000 km using the dispersion-managed optical transmission line is disclosed in Nonpatent literature 1. In this dispersion-managed optical transmission line, a positive-dispersion optical fiber having a wavelength dispersion of 20 ps/nm/km and an effective core area of 110 μm2 and a negative-dispersion optical fiber having a wavelength dispersion of 40 ps/nm/km and an effective core area of 30 μm2 at a wavelength of 1,550 nm are combined to suppress an accumulated dispersion in the optical transmission line to almost zero. Both of the optical fibers used in the dispersion-managed optical transmission line have a bending loss of equal to or smaller than 15 dB/m when the optical fibers are wound 16 times with a diameter of 20 mm.
As for the positive-dispersion optical fiber, a conventional optical fiber having a W-type refractive index profile is used, which includes an inner core portion, an outer core layer formed on an outer circumference of the inner core portion, with a refractive index lower than that of the inner core portion, and a cladding layer formed on an outer circumference of the outer core layer, with a refractive index higher than that of the outer core layer and lower than that of the inner core portion.
Nonpatent literature 1: J. -X. Cai, et al, OFC 2002, PD-FC4 (2002), “Transmission of Thirty-Eight 40 gigabits per second (Gb/s) Channels (>1.5 terabits per second (Tb/s)) Over Transoceanic Distance”